ci: Remove the need for an empty Piglit results file

Just create such an empty file if there isn't already.

So drivers that are expected to pass all tests don't need to commit an
empty results file.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10295>

.gitlab-ci/piglit/run.sh

@@ -244,9 +244,11 @@ if [ -n "$USE_CASELIST" ]; then
 
     grep -F -f /tmp/executed.txt "$INSTALL/$PIGLIT_RESULTS.txt" \
        > ".gitlab-ci/piglit/$PIGLIT_RESULTS.txt.baseline" || true
-else
+elif [ -f "$INSTALL/$PIGLIT_RESULTS.txt" ]; then
     cp "$INSTALL/$PIGLIT_RESULTS.txt" \
        ".gitlab-ci/piglit/$PIGLIT_RESULTS.txt.baseline"
+else
+    touch ".gitlab-ci/piglit/$PIGLIT_RESULTS.txt.baseline"
 fi
 
 if diff -q ".gitlab-ci/piglit/$PIGLIT_RESULTS.txt.baseline" $RESULTSFILE; then